OVERVIEW

This is the first chapter of Part I which deals with the way in which solar radiation drives energy and matter flows in the atmosphere and oceans and how these flows are linked to weather and climate. This chapter introduces you to some basic ideas about the earth, its rotation and revolution.

• The earth is shaped as an oblate ellipsoid because the earth's rotation causes it to bulge slightly at the equator.
• The earth rotates in an eastward direction.
• The earth's rotation is important for 5 reasons:
  • the axis of rotation is a reference for latitude and longitude.
  • it results in the daily cycle that the 24 hour day is based on.
  • it influences physical and life processes on earth
  • it produces the Coriolis effect which deflects the flow of fluids (air and water) to the left in the southern hemisphere and to the right in the northern hemisphere.
  • the tides result from the moon's gravitational pull on the side of the earth closest to the moon, creating a rise and fall of ocean water as the earth rotates.
• Latitude is the position of a given point in terms of its angular distance from the equator. Lines of latitude are parallel to each other and range from 0° to 90° north and south. The equator is the longest parallel of latitude and is located at 0°.
• Longitude is the measure of the position of a point eastward or westward from a reference meridian (the prime meridian at Greenwich, England). Lines of longitude are farthest apart at the equator and converge at the poles. Lines of longitude range from 0° at Greenwich, England to 180° east and west (the International Date Line).
• A map projection is a system for changing the curved/spherical geographic grid to a flat grid.
• The polar projection produces a map with true shapes of small areas.
• The Mercator projection shows true compass direction on any straight line on the map and is useful for showing the flow of winds and ocean currents as well as lines of equal air temperature and pressure.
• The Goode projection is an equal area projection useful for depicting geographical features that occupy surface areas.
• Standard meridians are usually spaced 15° apart representing a time difference of one hour.
• The earth revolves counterclockwise around the sun every 365¼ days in an elliptical orbit.
• The earth is closest to the sun at perihelion on approximately January 3 and farthest from the sun at aphelion on approximately July 4.
• The earth's axis is tilted 23½° and the north pole always points towards the north star, Polaris.
• The subsolar point is the point on the earth's surface where the sun is directly overhead and which receives the highest amounts of solar radiation.
• During the year, the subsolar point moves from the equator at the March equinox to the Tropic of Cancer at the June solstice, then back to the equator at the September equinox and to the Tropic of Capricorn during the December solstice.
• Two important facts about the Sun-Earth Energy Flow System are that half the earth is always receiving solar energy but all places on the earth's surface do not receive the same amount of energy.

KEY TERMS

oblate ellipsoid  standard time     tropic of cancer   
diurnal           zones             tropic of          
Coriolis effect   International     capricorn         
geographic grid   Date Line         arctic circle      
latitude          daylight saving   antarctic circle   
longitude         time              equator            
map projections   revolution        standard meridian  
polar projection  perihelion        declination        
Mercator          aphelion          cartography        
projection        solstice          solar day          
Goode projection  equinox                              
                  subsolar point                       
                  plane of the                         
                  elliptic                             

STUDY QUESTIONS

1. List the three environmental effects of the earth's rotation.
2. How do we know the earth is round?
3. Describe how the position of latitude 40°S is determined.
4. Describe the appearance and use of the polar projection.
5. How was the Mercator projection useful to sailors, how is it useful to geographers?
6. What useful properties does the Goode's projection have?
7. What problems do we encounter when using each of these projections?
8. Describe how the standard time zones were established.
9. What is perihelion, what is aphelion?
10. What is the impact of the earth's tilt being fixed with the north pole always pointing to Polaris?
11. How does the sun's declination vary throughout the year?